The long term objectives of this project are to use genetic and other approaches to identify new genes and gene products involved in HLA class II restricted antigen processing, and to determine how these gene products function. The specific aims of this application are: to determine by complementation analysis whether three new antigen processing mutants, two of which have been shown not to be DM mutants, are affected for the same or different genes; to clone the genes affected in these new antigen processing mutants and in additional mutants which are affected for new antigen processing genes; to further characterize the defects in the three new antigen processing mutants, by run-on transcription, transient expression of DM-reporter constructs, gel shift assays, DM mRNA stability and, when the affected genes are identified, by DNA and protein sequence analysis for domains and motifs informative regarding function, by expression of the protein products of the affected genes, and by the generation of antibodies to the products of the identified genes; to characterize the defects in the affected genes in other antigen processing mutants which define new genes; and to study some aspects of DM function, including characterization of HLA alleles and isotypes which function independently of DM in antigen presentation, and the mapping of functional regions of interaction of DM and class II molecules using transfection of mutated DM and DR genes into DM and DR mutants. The investigators believe that these studies will lead to the identification of new genes and gene products involved in class II restricted antigen processing and an understanding of their functions. Antigen processing has a central role in host defenses against microbial agents and is of likely importance in diseases of autoimmunity. Thus these basic studies should lead to a better understanding of host defense mechanisms, and of ways to enhance host defenses against microorganisms and to ameliorate autoimmune diseases.